During the working of aluminum such as in rolling mills, light mineral oils are often used, and to further improve metal surface quality and control the shape (flatness) of the sheet during the working process, certain additives are blended with the mineral oil. These additives usually consist of organic materials such as aliphatic acids, esters of aliphatic alcohols and aliphatic acids, aliphatic alcohols and many natural oils such as palm and coconut oils.
As the metal passes through the rolling mill rolls, it is reduced in thickness. During this process, oxides, already present on the entering metal are broken into tiny particles and enter the rolling lubricant. In addition, fresh metal particles or fines are formed by contact of the fresh metal with the rolls as well as by the gouging of the fresh metal with the hard oxide particles.
During the rolling process, the additive materials are gradually consumed through oxidation and by reaction with the metals. The mineral oil itself may slowly oxidize. Fresh oxide free metal is extremely active and is normally formed in the roll nip as the metal is reduced in thickness. Thus, the metal surface reacts with the additive material to form organic soaps-salts of the metal and organic acids. These soaps are very undesirable materials in that they tend to cling to the metal and cause surface defects as the metal undergoes further reduction in succeeding passes through the mill. Enormous sums of money have been spent by the industry in attempts to remove or minimize the amount of these soaps. Heretofore, the most common method for controlling soap and removing it from the coolant oil has been by filtration through a mixture of Fullers earth and diatomaceous earth, which are also used to filter particles of metal and metal oxide.
Because of environmental considerations, it has become increasingly difficult to dispose of the enormous quantities of used mixtures of earths since such mixtures contain small amounts of oil and additives. It is likely that in the near future, disposal of such quantities of untreated earth generated each day by the industry will be entirely prohibited. To solve this critical problem, a considerable effort has been made to develop a more satisfactory method of cleaning up used metal working lubricants.
In the prior art Riesmeyer (U.S. Pat. No. 2,339,520) disclosed an early attempt to accomplish this clean up process by treatment of the oils with concentrated sulfuric acid in an amount of 85% of the stoichiometric quantity required to react with all of the aluminum and its oxide.
However, it was found that concentrated sulfuric acid, a very potent material, when used with coolant oil such as a vegetable or mineral oil formed almost immediately a brownish, red sludge. Many other oils behaved similarly. This required a further complicated procedure involving separation of the sludge from the treated oil and ultimately disposal of the sludge material. Also the reaction produced in Riesmeyers' treatment caused the removal of beneficial additive materials from the coolant oil, because concentrated sulfuric acid inherently tends to attack numerous organic compounds. For the aforesaid reasons and also the fact that concentrated sulfuric acid is a dangerous material for production workers to handle, the Riesmeyer method proved to be impractical for actual use.
It is therefore a general object of the present invention to provide an improved process for filtering or reclaiming coolant oil used during the working of aluminum which will effectively remove contaminants such as aluminum fines, oxides and soaps from the oils.
Another object of the invention is to provide a process for reclaiming contaminated coolant oil which produces used filtration media that is non-toxic and can be disposed of without expensive labor intensive procedures.